Left atrium and ventricle

Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the left atrium and ventricle, another topic of the heart where we’re going to essentially explore this image that you see now on your screen. This is an image of the left lateral view of your heart where we just cut open here the left ventricle. We’re also going to cut open here and expose then the left atrium and then cover all these structures – all the important structures – that are related to the left atrium and ventricle.

Let’s start off with the very first structure here highlighted in green which is the left atrium and on this image – as you remember before – we’re highlighting it from a left lateral view while on this image, we’re highlighting it from now a right lateral view of the heart. And here we have the right atrium cut open but we still see here on the image for a bit of perspective, the left atrium highlighted in green.

The left atrium receives oxygenated blood from the pulmonary veins which you can also see here on this image, then pumps it into the left ventricle via the mitral valve which you also see here on the image that we’re going to be talking about it later on on this tutorial. There are a few roles that I would like to add here on this tutorial associated to the left atrium. The atria, in general, of the heart – atria meaning plural of atrium – will be facilitating circulation primarily by allowing uninterrupted venous flow to the heart preventing then inertia of interrupted venous flow that would otherwise occur at each ventricular systole.

Other structures that we’re going to be seeing here highlighted which I talked about before, these are the left pulmonary veins specifically. And the pulmonary veins are large blood vessels that will be receiving oxygenated blood from the lungs and drain it into then the left atrium of the heart. There are 4 pulmonary veins, 2 from each lung, and we see here 2 – so two left pulmonary veins. The pulmonary veins are among the very few veins that carry oxygenated blood.

The next very important structure that I talked about before – this is highlighted in green – the mitral valve, also known as the bicuspid valve or left atrioventricular valve which is a dual flap valve in the heart that lies between the left atrium and the left ventricle. This is a very, very important valve. Now, in terms of role, during diastole, a normally functioning mitral valve will be opening as a result of increased pressure from the left atrium as it fills with blood. Then what happens is that as atrial pressure increases above of the left ventricle, the mitral valve will then open. Opening of this valve will then facilitate the passive flow of blood into the left ventricle. Diastole ends with atrial contraction which ejects then the final 20% of blood that is then transferred from the left atrium to the left ventricle. The mitral valve then closes at the end of the atrial contraction and then to prevent reversal of blood flow.

The next structures we’re going to be highlighting here, these are known as the chordae tendineae, also known as tendinous cords or heartstrings. They are cord-like tendons that connect the papillary muscles to the mitral valve and the papillary muscles are these structures that you find here – these projections – these are the papillary muscles in which we will also be talking about on this tutorial. The chordae tendineae are approximately 80% collagen while the remaining 20% is made up of elastin and endothelial cells.

Next structure in line that we’re going to be highlighting here, this is known as the left atrial appendage. This structure is found on the upper part of the left atrium and is an ear-shaped muscular pouch. We can also, you probably heard this is also called the auricle with reference to its shape from the ear – the more technical name for ear is auricle.

The next structure we can clearly see here on the open atrium is the valve of the foramen ovale. It is basically a fold projecting into the left atrium from the margin of the foramen ovale in the fetus. When with beginning of inspiration, the blood pressure within the left atrium increases, the valve will be closing and its edges become adherent to the margin of the foramen ovale which then occludes it or closes it.

The next structure we’re going to be highlighting here is basically a wall that is separating the two atria, so, the interatrial septum that separates the left atrium from the right atrium. And you can also see here this image where we have the right atrium open and you can see also from the other side, the interatrial septum. Clinical note associated to the structure is that atrial septal defect is relatively a common heart malformation that occurs when the interatrial septum fails to develop properly.

The next structure we’re going to be highlighting – one of the important topics here on this tutorial – this is the left ventricle. Now, on the left image, we’re looking at it from a cut of the left lateral view of the heart while here on the right image, we’re looking at now the anterior view of the heart but you see here highlighted the left ventricle for a bit of location to see where it is located from the anterior view of the heart. In diastole, the left ventricle receives oxygenated blood from the left atrium. When systole starts, its muscle cells contract in order to then pump blood into the aorta and thus into the whole body. The left ventricle has thicker walls than the right because it needs to pump blood to most of the body while the right ventricle fills only the lungs. If we open the left atrium and remove the mitral valve, you can see now on this image the next structure that is here highlighted in green which is known as the aortic valve.

The aortic valve is one of the 2 semilunar valves of the heart and the other being then the pulmonary valve. The heart has 4 valves and the other 2 are the mitral valve which we covered here on this tutorial and the other one you find here on the other side of the heart which is then the tricuspid valve. The aortic valve normally has 3 leaflets – you can even count them here on this image 1, 2, 3 – this one lies between the left ventricle and the aorta. So you see here the aorta or a bit of the aortic arch. This structure also has a very important role that I would like to talk about. During ventricular systole, pressure will be rising in the left ventricle. When pressure in the left ventricle rises above the pressure in the aorta, the aortic valve will be opening then allowing blood to exit the left ventricle into the aorta. And when ventricular systole ends, pressure in the left ventricle rapidly drops. So, when the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to then close.

Now, the next structures we’re going to be seeing here highlighted in green on this 2 images, on the left one, we see the anterior papillary muscles and on the right one we see the posterior papillary muscle. Now, the papillary muscles are muscles that are located in the ventricles of the heart. Now, we’re looking at those that are found then on the left ventricle and they attach to the cusps of the atrioventricular valves. So, in this case, the mitral valve. They attach via these strings that we talked about before, the chordae tendineae. Now, these muscles have important roles. They contract to then prevent inversion or prolapse of the mitral valve and the tricuspid valve as well on the right side of the heart.

The next structures I would like to highlight here on this tutorial are known as the trabeculae carneae. They are round or irregular muscular columns which then project from the inner surface of the ventricles of the heart and a very important point here is that you shouldn’t confuse them with pectinate muscles – these are different structures that we cover on a separate tutorial. Now, the pectinate muscles are not covered on this tutorial because they are present on the right atrium and auricles of the heart. So, if you would like to know more about them, I suggest you see our tutorial on the right atrium and ventricle.

Now, these structures have important roles that we’re going to be highlighting here on this tutorial. The purpose of the trabeculae carneae is most likely to prevent suction that would occur with the flat surfaced membrane and thus impair the heart’s ability to pump efficiently. So, the trabeculae carneae also serve a function similar to that of the papillary muscles and that their contraction pulls on the chordae tendineae preventing inversion of the mitral and tricuspid valves that is that they are bulging towards the atrial chambers which would lead to subsequent leakage of blood into the atria. So, by action of the papillary muscles on the atrioventricular valves then backflow of blood from the ventricles into the atria is then prevented.

The next structure we’re going to be seeing also a wall here now for the ventricles – this is the interventricular septum. So, you also see here on this image on the right side, the highlight of the interventricular septum. The interventricular septum is the stout wall that separates those ventricles of the heart and this structure is also directed obliquely backward to the right and curved with the convexity towards the right ventricle. Now, the margins also correspond with the anterior and posterior longitudinal sulci.

Another structure I would like to pinpoint here and highlight, this is known as the pulmonary trunk or also known as the pulmonary artery and this one will be carrying deoxygenated blood from the heart to the lungs. So, as you can notice, this is one of the rare arteries other than the umbilical arteries in the fetus that will be carrying deoxygenated blood. And as you can see clearly here on this image, it is divided into 2 other arteries, the right pulmonary artery which you see here and the left pulmonary artery. I‘d like to take a closer look now at this one which is the right pulmonary artery.

The right pulmonary artery or right branch of the pulmonary artery is longer and larger than the left one. It runs horizontally to the right behind the ascending aorta and superior vena cava and in front of the right bronchus to the root of the right lung where it then divides into 2 branches. Now, this structure will be carrying deoxygenated blood to the right lung. And I can also show you here another image of the heart, this time from a right lateral view where you can also see here highlighted in green the right pulmonary artery.

The next one we’re going to be highlighting is then the left pulmonary artery or the left branch of the pulmonary artery. It is then shorter and somewhat smaller than the right one and this time passes horizontally in front of the descending aorta and left bronchus to then the root of the left lung where it divides into 2 branches. This artery will be then carrying deoxygenated blood to the left lung.

The next structure we’re going to be highlighting here on this image is known as the coronary sinus and this is a collection of veins that join together to form a large blood vessel that will be collecting blood from the heart muscle. It then delivers deoxygenated blood to the right atrium as to the superior vena cava and also the inferior vena cava.

The next structure worth highlighting here on this image is known as the aortic arch. This is part of the aorta that begins at the level of the upper border of the 2nd sternocostal articulation on the right side. And as you can see here on this image of the open thorax where we remove the lungs and the heart and left exposed here the aortic arch highlighted in green and then the thoracic aorta which is clearly seen here. To show you that the aortic arch runs first upward and then backward into the left in front of the trachea which you can also see here on this image – so this is the trachea. It is then directed backward on the left side of the trachea and finally passes downward on the left side of the body of the 4th thoracic vertebra at the lower border of which it becomes then continuous with the structure here which is known as the descending aorta.

Finally, on this tutorial, I just want to pinpoint here this structure which is known as the cardiac apex. Now, the apex of the heart is the lowest superficial part of the heart. It is directed downwards, forward and to the left and is overlapped by the left lung and pleura. This structure lies behind the 5th left intercostal space 8-9 cm from the mid-sternal line slightly medial to the mid-clavicular line.

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